1. Field of the Invention
The present invention relates to a keyless vehicle entry apparatus and, more particularly, to a keyless vehicle entry apparatus for automatically locking and unlocking a door on receiving a code signal consisting of electric waves from a transmitter.
2. Description of the Prior Art
Keyless vehicle entry apparatus designed to automatically lock or unlock a door on receiving a code signal of very weak electric waves from a transmitter have recently come into general use, in particular, for high-quality cars wherein such an apparatus replaces a conventional door locking device in which a key is used.
It is possible to provide such a keyless vehicle entry apparatus not only on a door with locking and unlocking functions but also with various additional functions such as, for example, opening and closing a trunk or a window, or warning of a possible car-theft, thereby providing many advantages for the driver or owner of the vehicle.
In such a conventional keyless vehicle entry apparatus, as exemplified by that shown in FIG. 28, a code signal consisting of electric waves (of 60 MHz in the example shown in FIG. 28) delivered from a transmission antenna 12 of a transmitter 10 is received by a pole antenna 16 for radio broadcast wave reception which is provided on the surface of a vehicle body 14, and the receiving signal is input to a divider 20 through a feeder line 18. The divider 20 divides the receiving signal into the outputs of a radio 22 and a keyless entry signal receiver 24.
As a result, a sound signal is output from the speaker 26 of the radio 22 and a control signal 28 for locking or unlocking a door is output from the keyless entry signal receiver 24.
Such a conventional keyless vehicle entry apparatus, however, which divides a receiving signal of the antenna for radio broadcast wave reception into two, causes a drop in the receiving sensitivity for radio broadcast waves by about 3 dB. Furthermore, since the antenna for radio broadcast wave reception is adjusted mainly for radio broadcasting frequency bands, in particular, for the FM band (76 to 90 MHz in Japan), adequate sensitivity is sometimes unobtainable for the carrier frequency (60 MHz) of the electric waves which are generally used for propagating a code signal in a keyless vehicle entry apparatus.
In addition, in a strong electric field zone, such as the vicinity of a transmitting station for FM broadcasts or TV broadcasts, a strong input jamming occurs, and this necessitates such countermeasures as filtering and trapping.
Thus, it is necessary to provide an antenna exclusively for use by the keyless vehicle entry apparatus for automatically locking and unlocking a door on receiving a code signal consisting of electric waves from a transmitter. However, though a pole antenna which projects outwardly from the vehicle body is superior in performance in its own way, it always remains a nuisance from the point of view of vehicle design.
Furthermore, such a pole antenna is disadvantageous in that it is subject to damage, tampering or theft and also in that the antenna tends to generate noise during high-speed driving. For these reasons, there has heretofore been a strong desire to eliminate the need for such pole antennas, and to thus provide a second pole antenna would be at variance with this desire.
One of the proposals made to eliminate such problems has been to provide a receiving loop antenna for a keyless vehicle entry apparatus on a molding located in the vicinity of the outside handle of a door (Japanese Patent Laid-Open No. 44861/1984).
This keyless vehicle entry apparatus is advantageous in that the electric waves from a transmitter can be positively received without changing the external form or appearance of a vehicle body.
Such an improved keyless vehicle entry apparatus, however, is comparatively low in sensitivity, and, in addition, it is necessary from the viewpoint of its directional characteristics to dispose a transmitting antenna in close proximity to (at a distance of about 10 cm from) the receiving loop antenna.
Thus, it is inconveniently impossible to enjoy the full advantage of the keyless vehicle entry apparatus which can automatically lock and unlock a door when the operator is standing at a certain distance from the vehicle body.